Phase transitions and polymorphism in phospholipids

Abstract

An assembly of phospholipids dispersed in water exhibits a variety of phases in a narrow temperature range, i.e., subgel L_c. phase, gel L_β. (or L_β) phase, interdigitated gel L_β1 phase, ripple gel P_β. phase, liquid crystalline L_α phase, cubic Q phase, hexagonal H_II phase, etc. The characteristics of the structures in these phases are discussed. Some of the phase transitions are considered in terms of the critical packing parameter developed by Israelachvili, Marčelja and Horn (Quart. Rev. Biophys, 13, 121 ((1980)). For much further consideration, heterogeneity in the bilayer structure of phospholipids should be taken into account. In connection with this nature, the importance of a sequential mechanism in the phase transitions of phospholipids is pointed out.